Among recent location positioning systems which specifies the locations of radio communication terminal units, e.g., cellular phone units, there is a system which operates based on the IS (Interim Standard) protocol. In this system, a cellular phone unit receives base station identification numbers (base-IDs) from several base stations, designates one of these base stations to be its communication base station, and sends the base-ID of the designated base station to a location information server.
The location information server, upon receiving the base-ID from the cellular phone unit, determines the approximate location of the telephone unit based on the received base-ID and sends assist information useful for the telephone unit to make access to GPS (Global Positioning System) satellites. The cellular phone unit, upon receiving the assist information from the location information server, makes access to GPS satellites based on the received assist information. This system is advantageous for each cellular phone unit to reduce its operation by making access to GPS satellites based on the assist information provided by the location information server, and also advantageous for minimizing the time expended before the commencement of the location positioning operation.
In the portable mobile telephone system of the CDMA (Code Division Multiple Access) scheme, it is stated in ARIB STD-T53 to enable cellular phone units to receive base-IDs from base stations through the paging channel. However, it is not stated to enable the reception of base-IDs through the traffic channel, and therefore the following problem arises.
When a cellular phone unit is instructed by the user to commence the data communication, the radio communication device of the telephone unit turns from the standby mode to the data communication mode and links to a contents server, for example, so that the telephone unit can commence the data communication. If the telephone unit is subsequently instructed by the user to commence the location positioning, it cannot receive the base-ID from the base station through the traffic channel and therefore it sends the base-ID, which has been received through the paging channel during the standby mode of the radio communication device before turning to the data communication mode, to a location information server.
Specifically, in one case, as shown in FIG. 10A, when a cellular phone unit 51 is instructed by the user to commence the data communication and instructed to commence the location positioning almost at the same time, it sends to a location information server 53 the base-ID of a base station 52a which is the proper base station of primary communication with it.
In another case, as shown in FIG. 10B, when the cellular phone unit 51 at one location within the area (shown by dotted circle P) of the base station 52a is instructed by the user to commence the data communication, moves to another location within the area (shown by dotted circle Q) of another base station 52b, and is instructed to commence the location positioning at the new location, it cannot send the base-ID of the proper base station 52b to the location information server 53, but sends the base-ID of the improper base station 52a which is the former communication base station before the movement. In consequence, the location information server 53 receives the base-ID of the improper base station 52a of the area where the telephone unit 51 is not present currently, instead of receiving the base-ID of the proper base station 52b of the area where the telephone unit 51 is present currently. It cannot determine the approximate location of the telephone unit 51 properly and sends improper assist information to the telephone unit 51. The telephone unit 51, upon receiving the improper assist information from the location information server 53, cannot make access to proper GPS satellites and thus cannot determine its location accurately.